Various horological shock absorber bearings are known to those skilled in the art. FIGS. 1 and 2 show a standard type of bearing currently used in numerous timepiece movements. The bearing 2, called a “double inverted cone” bearing, is disclosed for example in FR Patent No 1 532 798. This bearing is arranged at the end of the arbour 6 of a rotating wheel set 4. More specifically, the pivot 8 of arbour 6 is mounted in the hole in a pierced jewel 10 forming bearing 2. Bearing 2 is formed of a support 12 with a central aperture in the bottom thereof for the passage of arbour 6 of the rotating wheel set. Support 12 has a recess inside which a setting 14 is arranged. This setting carries the pierced jewel 10 and an endstone 16 located above the pierced jewel. The setting and two jewels are held inside the recess of support 12 by a spring device 18, which, in the variant shown in FIGS. 1 and 2, includes two elastic tongues abutting against the top surface of the endstone. This standard type of bearing is considered attractive, particularly owing to the presence of a top endstone of relatively large diameter. Indeed, the endstone contributes to the attractive appearance of the timepiece movement and may be considered a decorative element of the timepiece movement. Those skilled in the art appreciate this conventional type of bearing shown in FIGS. 1 and 2.
FIGS. 3 and 4 show another shock absorber bearing disclosed in EP Patent No 1 696 286. According to this second known embodiment, this bearing essentially differs from the conventional type described above in that the pierced jewel 10 and endstone 16A are assembled to a rigid central part 28 of a flat elastic device 22, i.e. extending into a general plane. The two jewels are thus suspended at the centre of the elastic device, whose elastic structure or spring 26 is capable of undergoing axial and radial elastic deformation, i.e. in a general horizontal plane and also in the longitudinal direction of arbour 6 of the rotating wheel set. This second embodiment has certain advantages relative to the conventional shock absorber bearing described above, which are set out in EP Patent Application No. 1 696 286.
The elastic device 22 is formed by a peripheral ring 28 resting on an annular projecting portion provided in the bottom of the recess in base 12A. The elastic structure 26 is formed of several arms defining as many spring elements, which extend in an arc of a circle between peripheral ring 24 and the central part 28 of elastic device 22. This central part has a central aperture in which the pierced jewel 10 is arranged. Endstone 16A, placed on the top surface of this central part, is held in place by a cap 30, which has securing brackets 32 which extend along the lateral surface of the central part. The cap can be driven or bonded onto this central part.
It will be noted that the elastic structure 26 has a relatively complex geometry with a plurality of spring arms connecting peripheral ring 24 to the rigid central part 28. Thus, elastic device 22 is preferably made by a LIGA technique known to those skilled in the art.
As is clear from FIGS. 3 and 4, the shock absorber bearing 20 has a non conventional visual appearance. Indeed, the top view shows the entire flat elastic structure 26 and the endstone 16A is only visible through the small central aperture in the cap 30. Thus, the diameter of the visible surface of this top jewel 16A is substantially equal to that of the pierced jewel 10, which is small. By comparing the devices 2 and 20 respectively shown in FIGS. 1 and 3, the observer will note the significant difference in the visual appearance of the two devices. As set out above, the endstone of a shock absorber bearing in a mechanical timepiece movement is ornamental in nature and is used to add value to the mechanical movement. Although bearing 20 has several technical advantages and a variety of functions, it thus has the problem of a significant reduction in the visible diameter of endstone 16A.
FIG. 5 shows a shock absorber bearing 42 according to a third prior art embodiment, as disclosed, in particular in CH Patent No. 254 854. Bearing 42 overcomes the problem of reduced endstone diameter in bearing 20 of the second prior art embodiment described above. Bearing 42 includes an elastic device 22A of small thickness which extends in a generally horizontal plane. Although it has quite a different structure to the elastic structure 26 of FIGS. 3 and 4, the elastic structure of device 22A also allows elastic deformation in a horizontal plane and thus a horizontal movement of pierced jewel 10. This elastic structure would also allow axial deformation. However, the embodiment of FIG. 5 does not take advantage of this feature of elastic device 22A, unlike the bearing 20 described above. Indeed, endstone 16 does not move integrally with the pierced jewel and hence the central part of the elastic device. This jewel 16, which has a relatively large diameter, is placed on a ring or strut 46 on the peripheral part of device 22A. A second elastic device 48 is provided to hold jewel 16 in place and to allow it to move axially. This device 48 is formed of elastic tongues 50 abutting against the domed top surface of jewel 16. Since elastic tongues 50 are spaced apart, bearing 42 allows jewel 16 to be seen in a top view through a large aperture, so that the visual appearance of bearing 42 is similar to that of the conventional bearing 2 shown in FIGS. 1 and 2. However, to obtain this attractive effect, which enhances the timepiece movement, bearing 42 includes two distinct elastic devices 22A and 48. The first elastic device is associated with the pierced jewel 10 whereas the second elastic device is associated with the top endstone 16. Bearing 42 is thus relatively complex and expensive.